1. Field of the Invention
The present invention relates to a suspension arm formed by press working a plate-shaped member.
2. Description of the Related Art
There are various types of suspensions such as a double wishbone type, a strut type, a multi-link type, a trailing arm type, and the like. Accordingly, there are various types of suspension arms forming the suspensions. There are various configurations of suspension arms such as an A-type arm, an L-type arm, an I-type arm and the like, as well as various structures for suspension arms such as a structure in which a pipe-shaped member or a steel plate is press worked, an aluminum forged structure, and the like.
As described above, there are various types of suspension arms, and among these, a suspension arm which is fabricated by press working a single steel plate will be described hereinafter. The structure disclosed in Japanese Utility Model Application Laid-Open No. 61-57009 is an example of such a suspension arm.
To describe this structure briefly, as illustrated in FIG. 22, a suspension arm 100 includes a main portion 100A, which has a substantially U-shaped cross-section open toward the bottom of the vehicle, and flange portions 100B, which are provided at the lower end portions of the main portion 100A and which are bent in the longitudinal direction of the vehicle in directions of moving away from one another. On the whole, the suspension arm 100 has a substantially heart-shaped open cross-sectional configuration. The suspension arm 100 is fabricated by press working a single steel plate, and, as can be seen when viewed from above, is a substantially V-shaped or A-type arm.
The suspension disclosed in the aforementioned publication is a strut-type suspension. More specifically, the vehicle inner side distal ends of the bifurcations of the suspension arm 100 are connected to a vehicle body member 104 via bushes 102 so as to be freely swingable. Further, the vehicle outer side end portion of the suspension arm 100 is connected to the lower end portion of an axle carrier 106 which supports a wheel. The lower end portion of a shock absorber 110, around which a coil spring 108 is disposed, is connected to the upper end portion of the axle carrier 106.
When the suspension arm 100 having the above-described configuration is used, the following drawbacks arise. When the vehicle is traveling, load in the longitudinal direction of the vehicle is input to the suspension arm 100 from the wheel. This load in the longitudinal direction of the vehicle works as a force which attempts to bend the suspension arm 100. In particular, a relatively large bending moment is applied to the flange portion 100B in the vicinity of the portion encircled and denoted by letter A in the figure. As a result, the maximum tensile stress due to bending is generated in a vicinity of portion A. Accordingly, in order to ensure the rigidity of the vicinity of portion A of the flange portion 100B, the rigidity of the suspension arm 100 must be increased. More specifically, countermeasures such as increasing the overall thickness of the plate must be devised. As a result, a drawback arises in that the weight of the suspension arm 100 increases.